3i2 BYZANTINE CHURCHES CHAP.
have effectually covered up any traces which might have given a clue to the original form of the building. In consequence any attempt at restoration must be of a very tentative character.
It is evident that there has been a serious movement in the structure due to the weight of the dome and the thrust of the dome arches, for the walls below the dome are bent outwards in a very pronounced manner. ' It was in order to check this movement that the flying buttress was applied to the apse, and in all probability the enormous thickness of the walls surrounding the central cross is due to the same cause. Had the walls originally been as thick as at present it is hard to imagine that movement could have taken place.
The axial line from east to west, passing through the doors of both narthexes, divides the present building into two dissimilar parts. We know that the parecclesion is a later addition, and if it be removed and the plan of the north side repeated to the south the resulting plan bears a striking resemblance to S. Sophia at Salonica (Fig. 101). The position of the prothesis and diaconlcon in particular is identical in the two churches.
Some proof that this was the original form of the building is given by the small chamber in the wall thickness between the church and the parecclesion. For it corresponds to the angle of the south fi aisle,' and on its west wall is a vertical break in the masonry which may be the jamb of the old door to the narthex.
This plan gives a narthex in five bays—the three centre ones low, the two outer covered by domes and leading to the 'aisles.' When the parecclesion was added, the south gallery and two bays of the inner narthex were swept away. The third door leading into the church was built up, and the present large domed bay added to the shortened narthex.
Traces of the older structure remain in the wall between the church and the parecclesion. The space already described, which originally opened from the passage at the higher level to the south cross-arm, corresponds in width both to the window above and to the space occupied by the doors below. At S* Sophia, Salonica, the side-arms are filled